The present invention relates to optical sensors, and in particular to pulse oximeter sensors.
Many types of optical sensors are used to measure physiological characteristics of a patient. Typically, an optical sensor provides emitted light which is then scattered through a portion of a patient""s tissue and detected. Various characteristics of a patient can be determined from analyzing such light, such as oxygen saturation, pulse rate, tissue bilirubin, etc.
Pulse oximetry is typically used to measure various blood flow characteristics including, but not limited to, the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and the rate of blood pulsations corresponding to each heartbeat of a patient. Measurement of these characteristics has been accomplished by use of a non-invasive sensor which scatters light through a portion of the patient""s tissue where blood perfuses the tissue, and photoelectrically senses the absorption of light in such tissue. The amount of light absorbed is then used to calculate the amount of blood constituent being measured.
The light scattered through the tissue is selected to be of one or more wavelengths that are absorbed by the blood in an amount representative of the amount of the blood constituent present in the blood. The amount of transmitted light scattered through the tissue will vary in accordance with the changing amount of blood constituent in the tissue and the related light absorption. For measuring blood oxygen level, such sensors have typically been provided with a light source that is adapted to generate light of at least two different wavelengths, and with photodetectors sensitive to both of those wavelengths, in accordance with known techniques for measuring blood oxygen saturation.
Known non-invasive sensors include devices that are secured to a portion of the body, such as a finger, an ear or the scalp. In animals and humans, the tissue of these body portions is perfused with blood and the tissue surface is readily accessible to the sensor.
Certain types of optical sensors are applied to a patient""s external tissue by way of an adhesive attachment, enabled by an adhesive layer on the sensor. During the monitoring of a patient, there is a need to remove the sensor to perform a site check of the tissue location, and this removal typically damages the adhesive layer. Furthermore, adhesive type sensors are often used with disposable type sensors where the photo emitter and the detector are mounted on a backing without the benefit of a rigid optical mount to maintain the emitter and detector""s separation relatively fixed, and thus the sensor is subject to motion induced artifacts that may adversely affect measurement accuracy.
There is therefore a need to improve the functionality of adhesive-type optical sensors.
The present invention provides an optical sensor having a cover layer, an emitter disposed on a first side of the cover, a detector disposed on the first side of said cover, and a plurality of stacked independent adhesive layers disposed on the same first side of the cover, wherein the top most exposed adhesive layer is attached to a patient""s skin. Thus, when the sensor is removed to perform a site check of the tissue location, one of the adhesive layers may also be removed and discarded, exposing a fresh adhesive surface below for re-attachment to a patient""s skin. The independent pieces of the adhesive layers can be serially used to extend the useful life of the product.
One aspect of the present invention is directed towards using a generally annulus-shaped adhesive layer that surround the emitter and the detector and thus avoids having any adhesive present between the emitter and the detector to minimize optical shunt, which is known to adversely affect measurement accuracy.
Another aspect of the present invention is directed towards using optical lenses made from a soft or compliant material such as an optically transparent PVC material to minimize tissue necrosis.
Another aspect of the invention is directed towards the use of a semi-rigid optical mount structure to hold the emitter and the detector in place to maintain the separation between the electro-optics (emitter and detector) relatively fixed and yet allow a certain minimal amount of torque and twisting to occur as the sensor is applied. The semi-rigid optical mount, by maintaining the separation relatively fixed reduces motion induced artifacts in the detected electro-optic signals, which may adversely interfere with measurement accuracy. For a further understanding of the nature and advantages of the present invention, reference should be made to the following description in conjunction with the accompanying drawings.